Oil coolers for internal combustion engines and the like have long been used for cooling the oil for more efficient lubrication. Heretofore, such oil coolers have not attempted to control either the oil flow rate or the coolant flow rate in response to the oil temperature so as to achieve a more efficient temperature in the lubricating oil. In the present invention, the oil is either cooled when it is too hot or warmed when it is too cold or neither cooled nor warmed when neither is required and the operation of the oil temperature regulator is controlled only by the temperature of the oil itself.
This means that if the entering oil flowing through the regulator is too cold for most efficient operation of the engine, it is not cooled but is allowed to receive heat in its passage through the engine. If, on the other hand, the oil is too hot, it is directed through a cooling portion of the regulator where the excess heat is removed. Where the oil is at the proper temperature, it is passed through the regulator in parallel large passages so as to reduce the pressure drop of the oil flowing through the regulator.